In semiconductor laser devices such as those used for DVD (Digital Versatile Disc) application, a light reflecting layer made of a dielectric layer is provided on the end face constituting the optical cavity of the laser chip. The light reflectivity of this light reflecting layer can be changed to achieve the optical power and reliability meeting the requirements of the optical disc drive.
Such a light reflecting layer can be made of a dielectric layer including a single layer film or a multilayer film. The dielectric layer can be made of such materials as SiO2, SixNy, Al2O3, AlN, TiO2, and ZrO2.
When laser light is emitted to the outside through such a dielectric layer, its surface tends to accumulate charges due to dielectric polarization because the laser light has high energy. Furthermore, the package member constituting the semiconductor laser device, the mounting material of the chip, the sealing gas, and the ambient atmosphere often include Si organic compounds and hydrocarbon compounds. In the case where the emission wavelength of laser light is as short as 500 nm or less, the light beam has high energy, and hence easily decomposes the volatile gas generated from Si organic compounds and hydrocarbon compounds. For instance, Si organic compounds such as siloxanes, which are polymers with (Si—O—Si) bonds, and silanols including (—Si—OH) bonds, are easily decomposed by light beams having an emission wavelength of 500 nm or less used for the next generation DVD application. The decomposed atoms such as Si and O, and their reaction products are likely to be adsorbed by the charge on the surface of the light output layer, and to form a deposit made of e.g. SiOx. Such a deposit varies the far field pattern (FFP) of the laser beam, which is important for optical disc application. Furthermore, the decrease of optical power and the variation of driving current occur, and degrade the reliability.
Thus, in a semiconductor laser module for the next generation DVD application, it is necessary to remove the contaminant source attached to the package components as much as possible, and to provide hermetic sealing to prevent the intrusion of external contaminants. This inevitably complicates the module assembly process.